Dictionary with limited number of types

Question

First, excuse the rather funny name of my question. I'm no native speaker and it took me 10 minutes to express my thoughts in these few characters.

What I'm trying to do is to create a dictionary in C# that allows the value to be either an int, a string or a bool. What first had come to my mind was using generics, but as far as I know, I can only define one type as possible value-type, not "be one of those". Using object would also be possible, but boxing seems to be quite a performance-killer.

Is there any way to do this?

Here's a sample of what has come to my mind:

Dictionary<string, (string, int, bool)> foo = new Dictionary<string, (string, int, bool)>();
foo.Add("key1", "Hello, World!"); //Correct - Value is a string
foo.Add("key2", 37); //Correct - Value is an int
foo.Add("key3", true); //Correct - Value is a boolean
foo.Add("key4", new Foobar()); //Compiler error - Value is a Foobar

My ultimate goal is to provide a library for other developers. This feature should enable them to define "variables" during runtime and give them a type.

Edit://Firefox' about:config page has something very close to what I want to achieve

Answer 1

Why not create a fresh new class which implements the IDictionary and uses a Dictionary as a private variable.

Then, in the add methods, you can provide your own logic and fail accordingly

Sample code

public class MyDic : IDictionary<object, object>
{
    private Dictionary<object, object> privateDic= new Dictionary<object,object>();


    public void Add(object key, object value)
    {
        if (value.GetType() == typeof(string))
            throw new ArgumentException();
        privateDic.Add(key, value);
    }
    //Rest of the interface follows
}